Conventional ring lasers are relatively large in size, typically occupying a cylindrical volume of three inches in diameter and four inches high. Smaller ring lasers are desirable, especially for ring lasers used in gyroscopes. Smaller ring lasers and ring laser gyroscopes could benefit from integrated unit chip technology fabrication. Some miniaturization has been accomplished by using an epitaxial semiconductor such as GaAs and GaAlAs to function both as the lasing medium and the cavity. This is done by cleaving the semiconductor along four facets which serve as the cavity reflecting surfaces for the laser beam. See "Grating-Coupled GaAs Single Heterostructure Ring Laser" by D. R. Scifres, R. D. Burhnam and W. Streifer, Applied Physics Letters, Vol. 28, No. 11, Jun. 1, 1976; and U.S. Pat. No. 4,792,962, issued Dec. 20, 1988, Miyauchi et al., "A Ring-Shaped Resonator Type Semiconductor Laser Device". One shortcoming with such devices is that the expensive lasing medium is used not only to form the gain region, but also to form the entire resonator cavity; however, the lasing medium is only necessary for the lasing action where optical gain is desired. Also the geometry of the lasing medium and of the cavity are constrained by each other, as is the material used for them. The fact that the lasing medium and the cavity are one and the same material and structure militates against enlarging the cavity to improve the laser gyroscope sensitivity since the lasing medium necessarily will be enlarged too. In addition, the coupled nature of the cavity and the laser medium increases the difficulty of forming a laser that can support bidirectional propagation modes (clockwise and counterclockwise), without mode competition. Further, since the entire crystal in such devices is also the laser gain medium, light amplification must take place throughout the entire extent of the optical path in the crystal, or the non-lasing portion of the medium will simply absorb the optical energy and suppress the ring laser action.
The laser medium and cavity can be decoupled to avoid some of these shortcomings for example by using an external cavity where a series of mirrors external to the laser constitute the cavity. See U.S. Pat. No. 4,405,236, issued Sep. 20, 1983, Mitsuhashi et al., "Semiconductor Ring Laser Apparatus". However, such external cavity arrangements are not well suited to miniaturization and the necessary precision alignment of the mirrors that define the ring cavity. Both the external and internal cavity designs provide optical outputs. The optical output signal must be converted to electrical output for further processing by external logic circuits.